1. Field of the Invention
The present invention relates to, for example, a microscope system that irradiates a specimen with illumination light, and acquires a specimen image formed based upon light reflected from the specimen, and an illumination intensity adjusting method for adjusting an illumination intensity of illumination light employed for the microscope system.
2. Description of the Related Art
A microscope system using a microscope apparatus that irradiates a specimen with light for an observation of the specimen has conventionally been used for an observation of a cell, and the like in a field of medicine or in a field of biology. In an industrial field, a microscope apparatus has also been used for various purposes, including a quality control of a metal structure, a research and development of a new material, and a test of an electronic device and a magnetic head. As a method of observing a specimen by use of a microscope system, there have been known a method in which the specimen is visually observed, and a method in which a specimen image is captured by using an imaging device such as a CCD camera, and the captured image is displayed on a monitor.
The observation method by use of the microscope system includes a bright-field observation and a dark-field observation. The bright-field observation is the most popular observation method. In this method, illumination light is applied to a specimen in a direction parallel to an optical axis of an objective lens, by which a contrast of an image is acquired based upon a difference in light transmittance, reflectivity, and color to form a specimen image, and then, an observer observes the specimen image. On the other hand, in the dark-field observation, illumination light that tilts with respect to the optical axis of the objective lens is applied to the specimen, by which the light passing through the specimen or reflected from the specimen (observation light) is acquired to form a specimen image, and then, the observer observes the specimen image. In the dark-field observation, refracting light that passes through the specimen and refracts, or scattering light that is reflected from the specimen and scatters, is used as the observation light to form the specimen image.
When the specimen is observed by selectively using the bright-field observation and the dark-field observation depending on the specimen, or when the specimen is observed by both the bright-field observation and the dark-field observation, the specimen can be magnified and observed, or the shape of the specimen can be observed. Since the dark-field observation can apply a contrast to a low-contrast specimen that is difficult to be observed in the bright field, in particular, the dark-field observation is suitable for an observation of a concavo-convex shape on the specimen, such as a flaw, in the industrial field, for example.
Japanese Unexamined Patent Publication No. 2003-149169 discloses a wafer defect examining device including a bright-field illumination system and a dark-field illumination system as a microscope system that can perform the above-mentioned bright-field observation and the dark-field observation. In the wafer defect examining device, the illumination system to be used is switched between the bright-field illumination system and the dark-field illumination system, or the bright-field illumination system and the dark-field illumination system are simultaneously used, whereby specimen images acquired by the respective illumination systems can be observed.